I’ve never thought about this one, but it sounds fun !
Who would throw the other in the pool : Sonic, because he loves annoying Antoine. Antoine tried too, once, but then he realized that Sonic can’t swim (assuming Sonic kept it from him of all the Freedom Fighters, to not look ridiculous). Sometimes Sonic gets so much on his nerves that he’d actually enjoy pushing him in the pool, but he never does it out of fear of seeing him drown.
Who is the better carer when the other is sick : Sonic, he isn’t nearly as anxious as Antoine and has a pretty good self-control. In these cases, even if he is worried, he stays calm and does what he has to do.
Who would force the other to do extreme sports with them : Sonic and Antoine would fight him with his sword if he drags him to do dangerous stuffs.
Who would cook the better romantic dinner : Antoine. Even if he wasn’t that great of a cook, he still wouldn’t want to die horribly by letting Sonic near the microwave.
Who would build the blanket fort in the living room : Sonic because of his playfulness. He’d be actually more calm under the blanket fort, and as a result Antoine would enjoy much more his company.
Who would have the best holiday ideas : Sonic. He travels a lot and has already visited a lot of places. Antoine would however fight him - again - if he drags him somewhere dangerous.
Who would need to clean out the other’s stuff to make room for their own : Again Sonic doesn’t have a long of belongings, and Antoine just has the bare minimum for Freedom Fighting. So neither.